The present invention relates to a multilayer injection molding machine capable of press fitting resins from a plurality of injection units to a cavity part within a metal mold, respectively, an injection unit connecting device therefor, and an injection molding method thereby.
In the manufacture of a molded product formed of a plurality of layers of resins or colors, an injection molding machine for press fitting the resin of each layer into a metal mold in order is generally adapted, but in recent years, a multilayer injection molding machine capable of press fitting the resins of all the layers into the metal mold by one operation has been developed and adapted so that the molding time can be shortened to improve the productivity.
The conventional multilayer injection molding machine is constituted, as shown in FIG. 6, by juxtaposing, every resin of each layer, a plurality of (for example, two) injection units 53, 53 each of which has a heating cylinder 51 capable of raising the internal temperature to a prescribed temperature or more and an extruding screw 52 provided rotatably within the heating cylinder 51, and connecting and integrating the injection units 53, 53 together through a nozzle member 54. In injection molding, the tip of the nozzle member 54 is brought into contact with the spool hole of a metal mold 55, and the resin from each injection unit, 53, 53 is then collected together in the nozzle member 54 and discharged through the tip, whereby the resin of each layer is simultaneously press fitted into the metal mold 55.
However, since the above-mentioned conventional structure having all the injection units 53, 53 connected and integrated to the nozzle member 54 is intended for an exclusive machine for a molded product having the number of layers corresponding to the number of units of the injection units 53, 53, it is required to introduce and a set a multilayer injection molding machine for every molded product having each number of layers. Thus, even if a single-layer injection molding machine, for example, was introduced, new introduction of a two-layer injection molding machine is necessary in addition to this machine when a two-layer molded product is required. Therefore, existing facility equipments such as an injection molding machine, carrying device, and the like can not be effectively utilized. In a factory having no sufficient setting space, particularly, the introduction is extremely difficult since an action such as layout change of each equipment or disposal of the existing injection molding machine with the lowest frequency of use is required in order to ensure the setting space.
In recent years, it is also desired, from the view point of material cost or effective use of resources, to manufacture a molded product in which a core layer resin of low quality or low cost is thoroughly or partially covered with a desired skin layer resin. Thus, the multilayer injection molding machine having the structure described above is used also to cover such a core layer resin with the skin layer resin. However, this molding machine has a problem in that it is difficult to more surely cover the core layer resin with the skin layer resin because the core layer resin is likely to be included to the skin layer resin at the start of press fitting.
Thus, an object of the present invention is to easily manufacture a molded product having an optional number of layers by use of existing facility equipments.
Further, another object of the present invention is to surely cover a core layer resin with a skin layer resin in the manufacture of a molded product having the core layer resin covered with the skin layer resin.
The present invention involves an injection unit connecting device for a multilayer injection molding machine capable of press fitting resins from a plurality of injection units to a cavity part formed by clamping metal mold, and this injection unit connecting device comprises a connecting device body provided on the metal mold, and a resin passage means provided on the connecting device body and having a plurality of resin passages allowing the cavity part to communicate with each injection unit described above.
Since the number of injection units can be optionally changed by changing the number of passages of the resin passages of the injection unit connecting device, a multilayer injection molding machine capable of forming a molded product having an optional number of layers can be provided. The design specifications of the connecting device body and the resin passage means are matched to an existing metal mold or injection molding machine, whereby the existing metal mold or injection molding machine can be utilized as it is to form a multilayer injection molding machine. Thus, a multilayer injection molding machine for an optional number of layers can be provided while existing facility equipments are effectively utilized.
The above-mentioned resin passage means has a first resin passage formed in the clamping direction of the metal mold and a second resin passage formed in the direction crossing the clamping direction.
Since the second resin passage is formed so as to cross the first resin passage formed in the clamping direction of the metal mold, the second resin passage can be determined toward, for example, a setting space having a vertical or horizontal room according to the equipment layout around the injection unit to be connected to the first resin passage. Thus, the existing injection molding machine can be changed into a multilayer injection molding machine for an optional number of layers without moving existing facility equipments.
The above-mentioned resin passage means also has a passage opening and closing means for opening and closing the resin passages. Since the opening and closing timing of the resin passages can be optionally set by the passage opening and closing means, the timings of start and termination of press fitting of each resin to the cavity part can be optionally set, and resin leakage can be also surely prevented.
The injection unit connecting device is integrated into a multilayer injection molding machine having an injection unit arranged in the clamping direction of the metal mold and an injection unit arranged in the direction orthogonal to the clamping direction. Thus, a multilayer injection molding machine having the structure in which each injection unit is arranged in the least obstructive orthogonal direction can be provided.
Further, the injection unit connecting device is integrated into an injection molding machine for forming a single-layer molded product so as to provide it with a plurality of injection units. Since the multilayer injection molding machine is formed by use of an existing single-layer injection molding machine, the introduction cost can be reduced.
The injection unit connecting device is also preliminarily provided on the metal mold. When a metal mold is newly manufactured, the injection unit connecting device is provided on the metal mold in advance, whereby the metal mold can be preliminarily manufactured in the state integrated with the injection unit connecting device. Therefore, only by replacing the metal mold, an existing single-layer injection molding machine or multilayer injection molding machine, for example, can be switched to a multilayer injection molding machine according to metal mold.
The present invention also involves a multilayer injection molding machine for forming a molded product having a core layer resin covered with a skin layer resin, and this multilayer injection molding machine comprises a metal mold for forming a cavity part, a core layer injection unit for press fitting the core layer resin to the cavity part through a core layer passage, a skin layer injection unit for press fitting the skin layer resin to the cavity part through a skin layer passage, and a passage opening and closing means for opening and closing the core layer passage.
The resin passage for the core layer resin is blocked at the start of press fitting of the skin layer resin, whereby the core layer resin can be prevented from being included into the skin layer resin. Since only the press fitting quantity of the core layer resin can be finely controlled by operating the resin passage for the core layer resin by the passage opening and closing means, the core layer resin can be press fitted in a desired ratio to the skin layer resin in press fitting. Thus, the core layer resin can be surely covered with the skin layer resin at the start of press fitting and in the full term of press fitting.
The above-mentioned multilayer injection molding machine further comprises the metal mold formed of a fixed mold fixed to a support member and a moving mold movable to the fixed mold so as to form a cavity part by clamping with the fixed mold, a connecting device body interposed between the fixed mold and the support member so as to fix the fixed mold to the support member, a resin passage means provided on the connecting device body and having the core layer passage and skin layer passage allowing the cavity part to communicate with each injection unit, and the passage opening and closing means provided on the connecting device body.
Thus, by matching the design specifications of the connecting device body and the resin passage means to an existing metal mold or injection molding machine, the existing metal mold or injection molding machine can be utilized as it is to form a multilayer injection molding machine. A multilayer injection molding machine for an optional number of layers can be thus provided while effectively utilizing existing facility equipments, and the core layer resin can be surely covered with the skin layer resin at the start of press fitting by the thus-obtained multilayer injection molding machine and in the full term of the press fitting thereby.
This invention further involves an injection molding method by a multilayer injection molding machine for forming a molded product having a core layer resin covered with a skin layer resin by press fitting the core layer resin and skin layer resin from the core layer injection unit and the skin layer injection unit to a cavity formed within the metal mold, respectively, and this injection molding method comprises a first process of press fitting the core layer resin together with the skin layer resin by opening a resin passage extending from the core layer injection unit to the cavity part, a second process of terminating the press fitting of the core layer resin within the press fitting period of the skin layer resin and blocking the resin passage once, and a third process of opening the resin passage again for a prescribed time so that the skin layer resin flows back to the resin passage.
The skin layer resin is actively made to flow back to the resin passage of the core layer resin, whereby only the skin layer resin is leaked even when a slight leakage or a slippage of timing of opening occurs in the resin passage of the core layer resin at the start of the following press fitting of the skin layer resin, so that the core layer resin can be surely prevented from being included into the skin layer resin. Thus, the core layer resin can be more surely covered with the skin layer resin.